Digital UV inkjet printing on three-dimensional plastic products is “ready for prime time.” Advancements in UV LED curing technology overcome many curing problems associated with traditional mercury vapor lamps. UV LED lamps are superior for curing low-viscosity UV inks on non-wettable, heat-sensitive polymeric and urethane/rubber substrates. However, not all the LEDs are constructed a similar or exhibit equal performance characteristics. This article is the first in a series to show process advancements for industrial led uv printer on plastics.
Until recently, UV LEDs are already confronted by technical and economic barriers that have prevented broad commercial acceptance. High cost and limited availability of LEDs, low output and efficiency, and thermal management problems – along with ink compatibility – were limiting factors preventing market acceptance. With advancements in UV LED technology, utilization of UV LEDs to treat could well be some of the most significant breakthroughs in inkjet printing on plastics.
Very easy to operate and control, UV LED curing has several advantages over mercury (Hg) vapor lamps. Small profile semiconductor devices are meant to last beyond 20,000 hours operating time (about 10 times longer) than UV lamps. Output is extremely consistent for too long periods. UV LED emits pure UV without infrared (IR), rendering it process friendly to heat-sensitive plastic substrates. Reference Table 1 UV LEDs vs. Mercury Vapor Lamps.
LED and Hg vapor bulbs have different emission spectra. Photoinitiators are matched towards the lamp, monomers, speed and applications. To achieve robust cure, LED requires different photoinitiators, and in turn, different monomer and oligomers inside the formulations.
Probably the most scrutinized regions of UV LED technology will be the maximum radiant power and efficiency produced. Ink curing necessitates concentrated energy to become shipped to the curable ink. Mercury Hg bulbs routinely have reflectors that focus the rays so the light is most concentrated with the ink surface. This greatly raises peak power and negates any competing reactions. Early LED lamps were not focused.
High power and efficiency are achievable with garment printer by concentrating the radiant energy through optics and packaging. High-power systems utilize grouping arrays of LED die. Irradiance is inversely proportional towards the junction temperature in the LED die. Maintaining a cooler die extends life, improves reliability and increases efficiency and output. Historical challenges of packaging UV LEDs into arrays happen to be solved, and alternative solutions can be found, dependant on application. A great deal of the development and adoption of LED technologies have been driven by electronic products and displays.
First, formulating changes and materials have already been developed, and also the vast knowledge continues to be shared. Many chemists now understand how to reformulate inks to complement the lamps.
Second, lamp power has increased. Diodes designs are improved, and cooling is more efficient so diodes get packed more closely. That, subsequently, raises lamp power, measured in watts per unit area with the lamp face, or better, with the fluid.
Third, lenses on lamp assemblies focus the strength, so peak irradiance is higher. The mix of the developments is making LED directly competitive, otherwise superior, to Hg bulbs in many applications.
Depending upon the application form and collection of inks, wavelength offerings typically include 365nm, 385nm and 395nm. Higher wavelengths are around for select chemistries. As wavelength boosts the output power, efficiency and expenses also scale, e.g., 365nm LEDs provide less output than 395nm LEDs.
The performance of your die is better at longer wavelengths, and the cost per watt output is lower while delivering more energy. Application history demonstrates that often 395nm solutions can effectively cure formulations more economically than 365nm alternatives. However, in some circumstances, 365nm or shorter wavelengths are required to achieve robust cure.
LED cure best complements digital inkjet printing. On reciprocating printheads, hot and high Hg bulbs require massive scanning system frames, that are not essential with LED. Fixed head machines have the print heads assembled in modules and installed in overlapping rows. The compact, cool UV lamp fits nicely attached to a head module. Further, digital printing often is short run with frequent stops, so immediate “On/Off” yields greater productivity and revenue.
There are 2 implementations of thermal management: water and air-cooling. Water cooling is certainly a efficient way of extracting heat, particularly in applications in which high power densities are required over large curing areas. With water cooling, lower temperatures can be had with higher efficiency and reliability.
A second advantage of water cooling is the compact UV LED head size, which permits integration where there is restricted space around the curing area. The drawbacks water cooling solutions dexjpky05 the heavier weight from the curing unit and added complexity and expenses for chillers and water piping.
The 2nd thermal management solution is air-cooling. Air-cooling inherently is less efficient at extracting heat from water. However, using enhanced airflow methods and optics yields successful air-cooling curing systems, typically approximately 12W per square centimeter. Some great benefits of air-cooled systems include ease of integration, lightweight, lower costs with no external chillers.
Maximization of A4 UV Printer output power is essential. Via selective optics, the vitality from LEDs may be delivered safer to the substrate or ink. Different techniques are included in integrated systems including reflection to focused light using lenses. Optics can be customized to meet specific performance criteria. As the OEM (end user) should not necessarily be worried about exactly how the optics are supplied inside the UV LED lamp, they must notice that suppliers’ expertise varies, and all UV LED systems are not created equal.